The inventive concept relates to semiconductor memories, and more particularly, the inventive concept relates to nonvolatile memory devices using a resistance material to store data, and to methods for driving nonvolatile memory devices using a resistance material to store data.
A memory cell of a nonvolatile memory device may utilize a material having a programmable and variable resistance characteristic (referred to herein simply as a “resistance material”) to store data. Examples of such devices include a phase change random access memory (PRAM), a resistive RAM (RRAM), a magnetic RAM (MRAM), among others. The mechanisms for setting a cell resistance vary among these types of device, but each is characterized by programming the cell resistance to represent (store) one or more bits of data.
For example, the PRAM utilizes the selective application of thermal energy to set (or reset) a phase change material thereof to a (relatively) crystal state or a (relatively) amorphous state. The phase change material in the crystal state has a lower resistance than that of the amorphous state has high resistance. Thus, stored data can be discriminated by determining a relative resistance of the memory cell. For example, the crystal state may be designated as set data or 0 data, and the amorphous state may be designated as reset data or 1 data.